The sphericity of the ball is measured through the comparison of its diameters in at least 16 directions. From the measurements obtained, we take the difference between the lesser measurement and the greater measurement to divide it by the average measurement of all the measured diameters. In this way we arrive at a parameter or coefficient of error for the measurement of the sphericity of the ball, from now on we will name it the sphericity tolerance (ST) of the ball.
The FIFA is the worldwide regulating entity for soccer and in its regulations it allows an (ST) of 2% for balls with the “inspected” seal and an (ST) of 1.5% for balls with the “approved” seal. For example, when making a soccer ball emulating the structure of planet Earth, the calculation of the sphericity would be the following: when subtracting the polar axis (12,714 km) from the equatorial axis (12,757 km), we obtain a difference of 43 km, which is divided by the average measurement of the diameter, to obtain an (ST) factor of less than 0.4%. This form of oblate spheroid that our planet adopts comes from its constant turning, which avoids its perfect sphericity, but maintains enough qualities to pass a hypothetical FIFA test.
In multipanel balls, a good distribution in the shape of the panels will guarantee a good result in the (ST) measurements, especially when a ball is measured after having been used for a game when the panels start to stretch because of the tension and internal forces of the structure. It is normal for tension to exist between the panels since we pretend to give a spherical form to a group of panels that where originally flat. Besides the form of the panels, an inadequate sewing procedure can negatively affect the (ST) sphericity results. Since it is difficult to control the human error, it is important to start the process with a group of panels that when put into practice will result in a ball having an improved sphericity. The technique considers that the improvements in sphericity of the balls used for ball games, allow the ball to behave in a more consistent way.
The improvements in sphericity of the panels emerged in the world cup Mexico 70, when the “bucky” ball (icosadodecahedron of 32 panels) was substituted for the then standard ball construction based on a cubic conformation of 18 panels. Two decades later new improvements are achieved in the (ST) through modifications carried out on the bucky ball with the introduction of the “Geo” ball, that consists in shortening three sides of the hexagon in order to achieve a considerable improvement in the sphericity is shown in U.S. Pat. No. 5,674,149. A further improvement was made in 1999 with the “Design for a compact ball” (Spanish Patent Office filing # 2,152,888). Through the patent of the present inventor U.S. Pat. No. 6,916,263 of 2005, as well as the introduction to the market of sewn designs such as the “Geo” and thermal-bonding molded designs such as the “Roteiro” and “Teamgeist”, the sphericity of the ball has been taken to factors nearing 100%.
According to the article “An exact method for the sphericity measurement of soccer balls” Neilson, et al., Proc. Instn. Mech. Engrs. Vol., 217, Part B; J. Engineering Manufacture, p. 715-719, 2003, the consistency in circumference and diameter does not guarantee a true sphericity of the ball since there are cases in which the ball adopts a constant lobed shape, that is not detected by traditional systems of measurement.
Some of the proposals for rearranging the panels described in U.S. Pat. No. 6,916,263 can form the lobed shapes described by Neilson. The present invention provides a means to correct this bulling, through a better distribution of the tension forces that operate within the basic spherical structure thereby providing a ball with a more nearly perfect sphericity. The new method also facilitates the formation of different types of spheroids having diverse characteristics.